1. Technical Field
The present disclosure relates to a semiconductor device having an integrated magnetic element and provided with a barrier structure against metal contamination, and to a method for manufacturing the semiconductor device. In particular, the semiconductor device includes a magnetic element and the barrier structure is designed to protect, during the manufacturing steps of the semiconductor device, the semiconductor device itself from metal contamination deriving from formation of the magnetic element. Moreover, the barrier structure also protects from metal contamination the equipment used during the steps of manufacturing the semiconductor device.
2. Discussion of the Related Art
In processes of micromachining of semiconductor wafers, in particular for the production of electronic devices, it is of fundamental importance to prevent or reduce metal contamination (typically, but not only, surface contamination) of the semiconductor wafer itself.
For example, integration of a thin ferromagnetic layer in a standard CMOS or CMOS-compatible process enables creation of integrated magnetic-field sensors, such as Fluxgate and Hall-effect sensors, which are able to detect external magnetic fields.
Contamination due to metal ions of the wafer being machined may be caused, for example, by the step of formation of the ferromagnetic layer and/or on account of contaminants already present in the deposition chamber due to previous manufacturing steps.
As is known, alloys with magnetic properties generally contain metals (such as, for example, iron, cobalt, platinum, molybdenum), which, in processes for manufacturing semiconductor devices, constitute contaminating elements for the devices themselves. However, numerous electronic devices or MEMS devices make use of magnetic elements formed in an integrated form with known steps of deposition and definition by selective etching (for example, but not only, Hall-effect sensors, DC-DC converters, transformers, etc.).
According to the known art, in order to reduce metal contamination of the wafer being machined there are carried out, for example, steps of surface etching of the wafer so as to remove any possible surface contaminants, and/or machinery is used for deposition/etching free from contaminants (or after verification that the contamination due to the above contaminants is lower than a certain tolerance threshold).
A method used for detecting the presence of metal contaminants is X-ray fluorescence (XRF) spectroscopy, or total-reflection X-ray fluorescence (TR-XRF) spectroscopy. The techniques of XRF or TR-XRF analysis are non-destructive techniques that make it possible to know the composition of a specimen analysed through study of the X-ray fluorescence emitted by the atoms of the specimen following upon excitation, which is typically obtained by irradiating the specimen with high-energy X and gamma rays.
However, it is evident that an analysis by means of XRF spectroscopy is a method control, and not prevention, of contamination. In addition, the confirmation of a contamination of the wafer beyond a minimum threshold means said wafer should be discarded.
Likewise, removal of metal contaminants by etching proves to be an invasive technique, which is not always usable and does not guarantee a complete elimination of the contaminants.
FIGS. 1-7 show manufacturing steps of a known type for the formation of a generic metal or magnetic element on a semiconductor wafer. The steps of FIGS. 2-6 entail a risk of contamination of the wafer and/or of the manufacturing equipment used during said step.
With reference to FIG. 1, a wafer 10 is provided made of semiconductor material, for example silicon, comprising a substrate 1. The substrate 1 may be of a previously machined type (in a way not shown in detail in FIG. 1) and may comprise, for example, electronic devices or portions (for example, implanted regions) of electronic devices designated by way of example by the reference number 9.
Once again with reference to FIG. 1, grown on the substrate 1 is an intermediate layer 2, for example an oxide layer. The intermediate layer 2 has a thickness for example of between 0.2 μm and 2 μm.
Then, FIG. 2, deposited (for example, by sputtering) on the wafer 10, in particular on the intermediate layer 2, is a layer 3 of magnetic (in particular, ferromagnetic) material, for example nickel-iron (NiFe), cobalt-iron-boron-silicon (CoFeSiB) or else cobalt-zirconium-tantalum (CoZrTa), or other magnetic material or magnetic alloy.
The step of FIG. 2 may entail a contamination of the wafer 10 by metal ions deriving from the step of formation of the magnetic layer 3. In particular, the contamination may regard a surface portion of the intermediate layer 2, but may extend even deep into the intermediate layer 2, as far as the substrate 1.
A possible solution could include the step of providing the intermediate layer 2 with a large thickness, but this would render more complex the provision of possible deep vias through the intermediate layer 2, in addition to increasing the thickness of the wafer 10 in an undesirable way.
The contamination deriving from metal ions may jeopardize even significantly operation of the electronic devices 9 in so far as undesirable metal ions concur in modifying the characteristics of conductivity of the regions in which they are present.
Then, FIGS. 3 and 4, a step of definition of the magnetic layer 3 is carried out, via a mask 4 made of photoresist or of some other material (e.g., “hard mask”).
The step of FIG. 3, where the mask 4 is formed on the wafer 10, may entail a contamination of the equipment used to form the mask, for example, in the case of a photoresist mask 4, of the equipment for spinning the photoresist and/or for photolithography in so far as in both steps the magnetic layer 3 is at least partially exposed.
Also the step of FIG. 4, where the magnetic layer 3 is removed selectively by wet etching or dry etching, may entail a contamination of the etching equipment. The step of FIG. 4 enables definition of the magnetic layer 3 so as to provide on the wafer 10 a magnetic element 3′ having a desired shape for the specific application.
Next (FIG. 5), the mask 4 is removed. Also this step may lead to a contamination of the etching equipment owing to removal of the mask 4, in so far as the magnetic layer 3 is exposed at the end of etching of the mask 4.
Next (FIG. 6), there follow subsequent steps of manufacture of the wafer 10, for example a step of passivation of the wafer 10 to protect the exposed magnetic element 3′. In a known way, a protective layer 6 is formed on the wafer 10, in particular over the magnetic element 3′ and alongside the magnetic element 3′. Also this step exposes the equipment used for formation of the protective layer 6 to risks of metal contamination in so far as the magnetic element 3′ is exposed during the step of formation (e.g., by passivation) of the protective layer 6.
Then (FIG. 7), this is followed by further manufacturing steps, for example opening of contacts 8 through the protective layer 6, designed, for instance, to provide an electrical contact from/to the magnetic element 3′.
It is evident from the description of the steps of FIGS. 2-6 that the risks of contamination of the wafer 10 and/or of the equipment used for manufacture thereof are multiple and can be difficult to control. Detection of the contamination of the equipment leads to suspension of use thereof awaiting a thorough cleaning step, with consequent obvious disadvantages.
In fact, ferromagnetic materials generally contain iron, nickel, cobalt, and other contaminating elements, which, in some cases, may lead to the failure of the electronic components 9 integrated in the wafer 10. Consequently, the wafers should be machined using dedicated equipment after deposition of the ferromagnetic material. The more technological steps are carried out after deposition of the ferromagnetic material, the greater the number of items of equipment that are used just for machining the wafers with the magnetic sensors, and the higher the costs involved.